How our memories become permanent

London: Scientists have for the first time identified a mechanism that regulates rhythmic brain waves that play a key role in making our memories permanent.

Memories undergo a consolidation process which stabilises and makes them become stronger -- a process where brain waves play an important role, the study said. 

The study revealed that one of the brain waves -- sharp wave ripples (SWRs) -- needed for consolidating memories is dominated by synaptic inhibition. 

It helps the brain set what an individual has learned or experienced as a quick instant replay.

SWRs is one among the three major brain waves coming from the hippocampus region of the brain that plays a key role in our memory making.

"Our results were able to show that precisely timed synaptic inhibition is the current generator for sharp wave ripples," said Peter Jonas, Professor at the Institute of Science and Technology Austria (IST Austria).

In the study, conducted in mice, the team set out to find the SWR mechanism -- whether ripples are caused by a temporal modulation of excitation or of inhibition at connecting points in brain cells, or synapses. 

The findings showed that the frequency of both excitation and inhibitor events at the synapse increased during the SWR.

But, synaptic inhibition was found to dominate over excitation during the production of SWRs, which means synaptic inhibition is responsible for forming the shape and rhythm of sharp wave ripples. 

Finally, the researchers also identified the neurons -- PV+ interneurons -- that provide inhibitory output onto other neurons and are mainly responsible for creating SWRs.

"Inhibition ensures the precise timing of neuronal firing. This could be critically important for preplay or replay of neuronal activity sequences and the consolidation of memory. 

"Inhibition may be the crucial player to making memories permanent," explained Jian Gan, post-doctoral student at IST Austria, in the paper published in the journal Neuron.